In a conventional technique, an increase in a temperature of intake air in an internal combustion engine is suppressed by connecting intake ports of a cylinder head respectively to branch pipes of an intake manifold via resin sleeves.
As regards connecting an intake port and an intake manifold via a sleeve, JP2007-056794A, published by the Japan Patent Office in 2007, proposes forming a space between the sleeve and a wall surface of the intake port so that a temperature on the wall surface of the intake port is less likely to be transmitted to intake air.
JP2009-052491A, published by the Japan Patent Office in 2009, further proposes forming a through hole in a wall surface of the sleeve, through which fuel that has accumulated in the space on the outside of the sleeve is discharged to the inside of the sleeve.